heya moda;
Are you overclocking your CPU or GPU, if you are overclocking your CPU and your AGP/PCI bus isnt locked at 66/33 you can get artifacts because todays graphics cards have little if any tolerance for increased bus frequency. If you arent overclocking then most likely the problem is due to heat, does your video memory modules have heatsinks on them? IF so then most likely you just need to replace your factory HSF with one that is more effective. I recommend comming into #Tomshardware IRC chat, the link for which can be found at the top of any community page, and talking to some of the guys, it takes much less time to figure out the problem since you can have a actual conversation with someone in real time, hope to see you soon.